Did Pirates Cure Seasickness?

[Alternate titles: Were Pirates Epileptic?  + Seasickness is flicker vertigo is photo epilepsy.]

I think they did.

So why did pirates wear eyepatches? Mythbusters says that it was for dealing with the low light of conditions below deck. I think it’s because seasickness is a mild type of photo epilepsy, and covering one eye helps mitigate seizures. Let me try to prove it to you.

Let’s start with some facts about photosensitive epilepsy: Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights; bold, regular patterns; or regular moving patterns.

  • For about 3% of people with epilepsy, exposure to flashing lights at certain intensities or to certain visual patterns can trigger seizures.
  • More common in children and adolescents.
  • Becomes less frequent with age.

So essentially, flickers cause seizures. But there is thing called flicker vertigo.

Flicker vertigo is an imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of a relatively bright light.” It is a disorientation-, vertigo-, and nausea-inducing effect of a strobe light flashing at 1 Hz to 20 Hz, approximately the frequency of human brainwaves. The effects are similar to seizures caused by epilepsy (in particular photosensitive epilepsy), but are not restricted to people with histories of epilepsy.

So…what if these are the same condition? Obviously nausea is not the same as a seizure, but seizures can cause nausea. Let’s keep looking. 

What is motion sickness? This is when people get sick in cars, planes, boats, space, and even in front of screens. The jury is still out on what causes it. Here are some facts people agree on.

  • It’s most common in children and pregnant women. 
  • It’s more common in people who get migraines. 
  • Asians are very susceptible. 
  • Medications can cause it.


  • One ear plug technique. Why in the world would this work?
  • Caffeine has shown to be effective against it. 
  • Closing your eyes has been shown to effective in mitigating symptoms. 


So seasickness is a type of motion sickness. How is this similar to photo epilepsy and flicker vertigo? If you look at the sky and ocean as contrasting patterns, the waves beneath you would create a “flicker” of sorts as your head bobs with the motion of the boat.

The frequency of ocean waves is 4-15 waves per minute And the boat will rock up and down on each wave. And every time your bobs, you’d see sky and ocean. And the faster the boat goes, and the more frequent the waves, the more people will find themselves hanging over the side. 

It would explain why staring at the horizon would help. It would help eliminate some or all of the person’s “flicker”.

And why cloudy days make things worse. The contrast with the sky and the water is greater, and more wind means more waves.

What about body language? This article tied seasickness to body sway. The scientist had people broaden their stances, and reduced their seasickness. It makes sense. The less you sway, the slower the sky/ocean cycles in your vision. But with this theory, he can only predict seasickness sixty percent of the time. Why? Because he ignores the other factor that seems to induce the same nausea: sounds.

So why would an ear plug help? Because your eyes are not the only things sensitive to these vibrations. Ocean waves have infrasonic sound frequencies from 0.4 to 16 hz.

Deaf people do not get motion sickness. This is important, but only to show that when the brain is impaired, you don’t get nauseous. So the nausea is a healthy reaction to the stimuli.

Why would pregnant women get motion sickness more often? They have added physical and mental stress. And the physical stress is the key. The baby bump changes the mother-to-be’s center of gravity, making them less stable, and more prone to swaying.

In summary, seasickness is a type of photo epilepsy. Pirates didn’t just wear eyepatches because it made them look tough, or so they could see in the dark. They wore them to prevent abdominal seizures that we call seasickness. 


  1. https://www.diversalertnetwork.org/health/ears/seasickness-or-motion-sickness
  2. http://mentalfloss.com/article/52493/why-did-pirates-wear-eye-patches
  3. https://en.wikipedia.org/wiki/Photosensitive_epilepsyhttps://en.wikipedia.org/wiki/Flicker_vertigo
  4. http://www.madsci.org/posts/archives/2004-11/1101806651.Es.r.html
  5. http://www.bbc.com/future/story/20160818-how-do-you-beat-seasickness
  6. https://www.flkeysnews.com/sports-outdoors/outdoors/diving/article79625597.html
  7. http://mentalfloss.com/article/69578/why-do-some-sounds-make-people-sick
  8. http://aqua4balance.com/healing-power-of-nature/the-sea/sea-waves-sound-effects.html
  9. https://www.scientificamerican.com/article/finding-balance-seasickness/
  10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5378784/
  11. https://en.wikipedia.org/wiki/Motion_sickness
  12. https://www.vox.com/2015/8/9/9121583/motion-sickness-carsick
  13. https://www.atrainceu.com/course-module-short-view/1473436-79_migraine-headaches-module-03
  14. https://www.theatlantic.com/health/archive/2015/02/the-mysterious-science-of-motion-sickness/385469/
  15. https://www.rd.com/health/wellness/motion-sickness-cause/
  16. https://www.medicalnewstoday.com/articles/176198.php
  17. https://www.ncbi.nlm.nih.gov/pubmed/8825456
  18. http://www.abc.net.au/science/articles/2010/08/09/2977608.htm
  19. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5008705/